The three dimensional structure of a crystalline complex containing actinomycin D and deoxyguanosine has shed light on the stereochemistry of actinomycin binding to DNA. The phenoxazone ring system of actinomycin intercalates into the DNA helix, while deoxyguanosine residues interact with both cyclic peptides through specific hydrogen bonds. This research proposal describes further work in progress with actinomycin as well as with other drugs and antibiotics known to associate with DNA.